Signal format that facilitates easy scalability of data streams

ABSTRACT

A computer readable medium having a data packet stored therein for causing a functional change in the operation of a device is disclosed. In one embodiment, the data packet is comprised of a scalably encoded data portion. In the present embodiment, the data packet further includes a header data portion corresponding to the scalably encoded data portion. The header data portion includes information adapted to be used by a transcoder to transcode the scalably encoded data portion.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a Continuation-in-Part of the copending, commonly-owned U.S. patent application Ser. No. 09/849,216, filed May 4, 2001, by Susie J. Wee et al., and entitled “Signal Format That Facilitates Easy Scalability Of Encrypted Streams.”

TECHNICAL FIELD

The present claimed invention relates to the field of streaming media. More specifically, the present claimed invention relates to the encoding and decoding of data.

BACKGROUND ART

Wireless streaming environments present many challenges for the system designer. For instance, clients can have different display, power, communication, and computational capabilities. In addition, wireless communication links can have different maximum bandwidths, quality levels, and time-varying characteristics. A successful wireless video streaming system must be able to stream video to heterogeneous clients over time-varying wireless communication links, and this streaming must be performed in a scalable manner. Scalability is needed to enable streaming to a multitude of clients with different device capabilities.

In order to achieve scalability and efficiency in wireless streaming environments, one must be able to easily adapt or transcode the compressed video stream at intermediate network nodes. A transcoder takes a compressed video system as the input, then processes it to produce another compressed video stream as the output. Sample transcoding operations include bitrate reduction, rate shaping, spatial downsampling, frame rate reduction, and changing compression formats. Network transcoding can improve system scalability and efficiency, for example, by adapting the spatial resolution of a video stream for a particular client's display capabilities or by dynamically adjusting the bitrate of a video stream to match a wireless channel's time-varying characteristics.

While network transcoding facilitates scalability in video streaming systems, it also presents a number of challenges. First, while computationally efficient transcoding algorithms have been developed, even these are not well-suited for processing hundreds or thousands of streams at intermediate wired network nodes or even a few streams at intermediate low-power wireless networking relay nodes. Furthermore, many prior art network transcoding methods impose severe encryption, decryption, and re-encryption schemes for the streamed data.

More specifically, in conventional video streaming approaches employing application-level encryption, video is first encoded into a bitstream using interframe compression algorithms. These algorithms include, for example, the Moving Picture Experts Group (MPEG) standard, the International Telecommunications Union (ITU) standard, H.263, or intraframe compression algorithms such as, for example, the Joint Photographic Experts Group (JPEG) or JPEG2000 standards. The resulting bitstream is then encrypted, and the resulting encrypted stream is packetized and transmitted over the network using a transport protocol such as unreliable datagram protocol (UDP). Prior Art FIG. 1 is a block diagram 100 which illustrates the order in which conventional application-level encryption is performed (i.e. Encode 102, Encrypt 104 and Packetize 106). One difficulty with this conventional approach arises when a packet is lost. Specifically, error recovery is difficult because without the data from the lost packet, decryption and/or decoding may be difficult if not impossible.

Prior Art FIG. 2 is a block diagram 200 illustrating another conventional secure video streaming system that uses network-level encryption (i.e. Encode 202, Packetize 204, and Encrypt 206). The system of Prior Art FIG. 2 can use the same video compression algorithms as the system of Prior Art FIG. 1. However, in the system of Prior Art FIG. 2, the packetization can be performed in a manner that considers the content of the coded video and thus results in better error recovery, a concept known to the networking community as application-level framing. For example, a common approach is to use MPEG compression with the RTP transport protocol which is built on unreliable datagram protocol (UDP), RTP provides streaming parameters such as time stamps and suggests methods for packetizing MPEG payload data to ease error recovery in the case of lost or delayed packets. However, error recovery is still difficult and without data from a lost packet, decryption and/or decoding is still difficult if not impossible.

Both of the conventional approaches of Prior Art FIG. 1 and Prior Art FIG. 2 are secure in that they transport the video data in encrypted form. However, with these conventional approaches, if network transcoding is needed, it must be performed in accordance with the method of Prior Art FIG. 3. That is, as shown in block diagram 300, the necessary transcoding operation is a decrypt 302, decode 304, process 306, re-encode 308, and re-encrypt 310 process. As shown in the block diagram 400 of Prior Art FIG. 4, in another conventional approach, the computational requirements of the operation of Prior Art FIG. 3 are reduced to a decrypt 402, transcode 404, and re-encrypt 406 process. Specifically, this computational reduction is achieved by incorporating and efficient transcoding algorithm (i.e. transcode module 404) in place of the decode 304, process 306, and re-encode 308 modules of Prior Art FIG. 3. However, even such improved conventional transcoding algorithms have computational requirements that are not well-suited for transcoding many streams in a network node. Hence, conventional schemes employing such encryption methods further reduce computational and streaming efficiency.

As yet another concern, wireless streaming systems are limited by wireless bandwidth and client resources. Wireless bandwidth is scarce because of its shared nature and the fundamental limitations of wireless spectrum. Client resources are often practically limited by power constraints and by display, communication, and computational capabilities. As an example, wireless transmission and even wireless reception alone typically consume large power budgets. In order to make the most efficient use of wireless bandwidth and client resources, it is desirable to send clients the lowest bandwidth video streams that match their display and communication capabilities. In wireless streaming systems where a sender streams video to a number of heterogeneous clients with different resources, network transcoders can be used to help achieve end-to-end system efficiency and scalability.

In hybrid wired/wireless networks, it is often necessary to simultaneously stream video to fixed clients on a wired network and to mobile clients on a wireless network. In such a hybrid system, it may often be desirable to send a full-bandwidth, high-resolution video stream to the fixed wired client, and a lower-bandwidth, medium-resolution video stream to the mobile wireless receiver. Conventional video streaming approaches, however do not achieve the efficiency and scalability necessary to readily accommodate the video streaming corresponding to hybrid wired/wireless networks.

Yet another example of the drawbacks associated with conventional video streaming approaches is demonstrated in conjunction with wireless appliance networks. In many wireless appliance networks, mobile senders and receivers communicate with one another over wireless links. A sender's coverage area is limited by the power of the transmitted signal. Relay devices can be used to extend the wireless coverage area when intended receivers are beyond the immediate coverage area of the sender. However, in the case of heterogeneous clients within the same wireless network, it may be desired to provide a higher bandwidth, high-resolution video stream to the high power wireless receivers, and a lower bandwidth, low-resolution video stream to the low power wireless receivers. Once again, conventional video streaming approaches, however do not achieve the efficiency and scalability necessary to readily accommodate such video streaming demands in wireless appliance networks. Although the above-listed discussion specifically mentions the shortcomings of prior art approaches with respect to the streaming of video data, such shortcomings are not limited solely to the streaming of video data. Instead, the problems of the prior art span various types of media including, but not limited to, audio-based data, image-based data, graphic data, web page-based data, and the like.

Accordingly, what is needed is a method and/or system that can stream media data in a computationally efficient manner. What is also needed is a method and/or system that can satisfy the above need and that can also stream media data to heterogeneous clients (“receiving nodes”) that may have different display, power, communication and computational capabilities and characteristics. The present invention provides a novel solution to these needs.

DISCLOSURE OF THE INVENTION

The present invention provides, in one embodiment, a data packet format which enables scalable encoding, transcoding, and decoding of data.

Specifically, in one embodiment, the present invention is comprised of a computer readable medium having a data packet stored therein for causing a functional change in the operation of a device is disclosed. In one embodiment, the data packet is comprised of a scalably encoded data portion. In the present embodiment, the data packet further includes a header data portion corresponding to the scalably encoded data portion. The header data portion includes information adapted to be used by a transcoder to efficiently transcode the scalably encoded data portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:

PRIOR ART FIG. 1 a block diagram which illustrates the order in which conventional application-level encryption is performed.

PRIOR ART FIG. 2 is a block diagram which illustrates another conventional secure streaming system using network-level encryption.

PRIOR ART FIG. 3 is block diagram illustrating a conventional transcoding method.

PRIOR ART FIG. 4 is block diagram illustrating another conventional transcoding method.

FIG. 5 is a schematic diagram of an exemplary computer system used to perform steps of the present method in accordance with various embodiments of the present claimed invention.

FIG. 6 is a flow chart of steps performed in a secure and scalable encoding method in accordance with one embodiment of the present claimed invention.

FIG. 7 is a block diagram of an encoding system in accordance with one embodiment of the present claimed invention.

FIG. 8 is a block diagram of an encoding system having a video prediction unit (VPU) coupled thereto in accordance with one embodiment of the present claimed invention.

FIG. 9 is a block diagram of an encoding system having a video prediction unit (VPU) integral therewith in accordance with one embodiment of the present claimed invention.

FIG. 10A is a schematic depiction of a frame of video data in accordance with one embodiment of the present claimed invention.

FIG. 10B is a schematic depiction of the frame of video data of FIG. 10A after segmentation into corresponding regions in accordance with one embodiment of the present claimed invention.

FIG. 10C is a schematic depiction of the frame of video data of FIG. 10A after segmentation into corresponding non-rectangular regions in accordance with one embodiment of the present claimed invention.

FIG. 10D is a schematic depiction of the frame of video data of FIG. 10A after segmentation into corresponding overlapping non-rectangular regions in accordance with one embodiment of the present claimed invention.

FIG. 11 is a flow chart of steps performed in decoding data which has been securely and scalably encoded in accordance with one embodiment of the present claimed invention.

FIG. 12 is a block diagram of a decoding system in accordance with one embodiment of the present claimed invention.

FIG. 13 is a block diagram of a decoding system having a video prediction unit (VPU) coupled thereto in accordance with one embodiment of the present claimed invention.

FIG. 14 is a block diagram of a decoding system having a video prediction unit (VPU) integral therewith in accordance with one embodiment of the present claimed invention.

FIG. 15A is a block diagram of an exemplary hybrid wired/wireless network upon which embodiments of the present invention may be practiced.

FIG. 15B is a block diagram of an exemplary wireless network upon which embodiments of the present invention may be practiced.

FIG. 16 is a block diagram of a source node, an intermediate (transcoder) node, and a receiving node in accordance with one embodiment of the present invention.

FIG. 17 is a block diagram of one embodiment of a transcoder device upon which embodiments of the present invention may be practiced in accordance with one embodiment of the present claimed invention.

FIGS. 18A, 18B, 18C, 18D and 18E are data flow diagrams illustrating various embodiments of a method for transcoding data packets in accordance with one embodiment of the present claimed invention.

FIG. 19 is a flowchart of the steps in a process for transcoding data packets in accordance with one embodiment of the present claimed invention.

FIG. 20 is a schematic representation of a data packet including header data and scalably encoded, progressively encrypted data in accordance with one embodiment of the present claimed invention.

FIG. 21 is a schematic representation of a data packet including scalably encoded, progressively encrypted data in accordance with one embodiment of the present claimed invention.

FIG. 22 is a flow chart of steps performed in a scalable encoding method in accordance with one embodiment of the present claimed invention.

FIG. 23 is a block diagram of an encoding system in accordance with one embodiment of the present claimed invention.

FIG. 24 is a block diagram of an encoding system having a video prediction unit (VPU) coupled thereto in accordance with one embodiment of the present claimed invention.

FIG. 25 is a block diagram of an encoding system having a video prediction unit (VPU) integral therewith in accordance with one embodiment of the present claimed invention.

FIG. 26A is a schematic depiction of a frame of video data in accordance with one embodiment of the present claimed invention.

FIG. 26B is a schematic depiction of the frame of video data of FIG. 26A after segmentation into corresponding regions in accordance with one embodiment of the present claimed invention.

FIG. 26C is a schematic depiction of the frame of video data of FIG. 26A after segmentation into corresponding non-rectangular regions in accordance with one embodiment of the present claimed invention.

FIG. 26D is a schematic depiction of the frame of video data of FIG. 26A after segmentation into corresponding overlapping non-rectangular regions in accordance with one embodiment of the present claimed invention.

FIG. 27 is a flow chart of steps performed in decoding data which has been scalably encoded in accordance with one embodiment of the present claimed invention.

FIG. 28 is a block diagram of a decoding system in accordance with one embodiment of the present claimed invention.

FIG. 29 is a block diagram of a decoding system having a video prediction unit (VPU) coupled thereto in accordance with one embodiment of the present claimed invention.

FIG. 30 is a block diagram of a decoding system having a video prediction unit (VPU) integral therewith in accordance with one embodiment of the present claimed invention.

FIG. 31A is a block diagram of an exemplary hybrid wired/wireless network upon which embodiments of the present invention may be practiced.

FIG. 31B is a block diagram of an exemplary wireless network upon which embodiments of the present invention may be practiced.

FIG. 32 is a block diagram of a source node, an intermediate (transcoder) node, and a receiving node in accordance with one embodiment of the present invention.

FIG. 33 is a block diagram of one embodiment of a transcoder device upon which embodiments of the present invention may be practiced in accordance with one embodiment of the present claimed invention.

FIGS. 34A, 34B, 34C and 34D are data flow diagrams illustrating various embodiments of a method for transcoding data packets in accordance with one embodiment of the present claimed invention.

FIG. 35 is a flowchart of the steps in a process for transcoding data packets in accordance with one embodiment of the present claimed invention.

FIG. 36 is a schematic representation of a data packet including header data and scalably encoded data in accordance with one embodiment of the present claimed invention.

FIG. 37 is a schematic representation of a data packet including scalably encoded data in accordance with one embodiment of the present claimed invention.

The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.

BEST MODES FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “receiving”, “segmenting”, “scalably encoding”, “progressively encrypting” or the like, refer to the actions and processes of a computer system, or similar electronic computing device. The computer system or similar electronic computing device manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission, or display devices. The present invention is also well suited to the use of other computer systems such as, for example, optical and mechanical computers.

Computer System Environment of the Present Scalable Streaming Invention

With reference now to FIG. 5, portions of the present interrupt events chaining method and system are comprised of computer-readable and computer-executable instructions which reside, for example, in computer-usable media of a computer system. FIG. 5 illustrates an exemplary computer system 500 used in accordance with one embodiment of the present scalable streaming invention. It is appreciated that system 500 of FIG. 5 is exemplary only and that the present invention can operate on or within a number of different computer systems including general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, stand alone computer systems, and the like. Additionally, computer system 500 of FIG. 5 is well adapted having computer readable media such as, for example, a floppy disk, a compact disc, and the like coupled thereto. Such computer readable media is not shown coupled to computer system 500 in FIG. 5 for purposes of clarity.

System 500 of FIG. 5 includes an address/data bus 502 for communicating information, and a central processor unit 504 coupled to bus 502 for processing information and instructions. Central processor unit 504 may be an 80×86-family microprocessor. System 500 also includes data storage features such as a computer usable volatile memory 506, e.g. random access memory (RAM), coupled to bus 502 for storing information and instructions for central processor unit 504, computer usable non-volatile memory 508, e.g. read only memory (ROM), coupled to bus 502 for storing static information and instructions for the central processor unit 504, and a data storage unit 510 (e.g., a magnetic or optical disk and disk drive) coupled to bus 502 for storing information and instructions. System 500 of the present invention also includes an optional alphanumeric input device 512 including alphanumeric and function keys coupled to bus 502 for communicating information and command selections to central processor unit 504. System 500 also optionally includes an optional cursor control device 514 coupled to bus 502 for communicating user input information and command selections to central processor unit 504. System 500 of the present embodiment also includes an optional display device 516 coupled to bus 502 for displaying information.

Referring still to FIG. 5, optional display device 516 of FIG. 5, may be a liquid crystal device, cathode ray tube, or other display device suitable for creating graphic images and alphanumeric characters recognizable to a user. Optional cursor control device 514 allows the computer user to dynamically signal the two dimensional movement of a visible symbol (cursor) on a display screen of display device 516. Many implementations of cursor control device 514 are known in the art including a trackball, mouse, touch pad, joystick or special keys on alphanumeric input device 512 capable of signaling movement of a given direction or manner of displacement. Alternatively, it will be appreciated that a cursor can be directed and/or activated via input from alphanumeric input device 512 using special keys and key sequence commands. The present invention is also well suited to directing a cursor by other means such as, for example, voice commands. A more detailed discussion of the present scalable streaming invention is found below.

General Description of the Present Secure Scalable Streaming Invention

With reference next to FIG. 6, FIG. 11, and FIG. 19, flow charts 600, 1100, and 1900, respectively, illustrate exemplary steps used by the various embodiments of present invention. Flow charts 600, 1100, and 1900 includes processes of the present invention which, in one embodiment, are carried out by a processor under the control of computer-readable and computer-executable instructions. The computer-readable and computer-executable instructions reside, for example, in data storage features such as computer usable volatile memory 506, computer usable non-volatile memory 508, and/or data storage device 510 of FIG. 5. The computer-readable and computer-executable instructions are used to control or operate in conjunction with, for example, central processing unit 504 of FIG. 5.

As an overview, the present invention is directed towards any data which can be scalably encoded and, specifically, any data that combines scalable encoding with progressive encryption. For purposes of the present Application, scalable coding is defined as a process which takes original data as input and creates scalably coded data as output, where the scalably coded data has the property that portions of it can be used to reconstruct the original data with various quality levels. Specifically, the scalably coded data is often thought of as an embedded bitstream. The first portion of the bitstream can be used to decode a baseline-quality reconstruction of the original data, without requiring any information from the remainder of the bitstream, and progressively larger portions of the bitstream can be used to decode improved reconstructions of the original data. For purposes of the present Application, progressive encryption is defined as a process which takes original data (plaintext) as input and creates progressively encrypted data (ciphertext) as output, where the progressively encrypted data has the property that the first portion can be decrypted alone, without requiring information from the remainder of the original data; and progressively larger portions can be decrypted with this same property, in which decryption can require data from earlier but not later portions of the bitstream.

Encoding Method and System

Although specific steps are disclosed in flow chart 600 of FIG. 6, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 6. Additionally, for purposes of clarity and brevity, the following discussion and examples will specifically deal with video data. The present invention, however, is not limited solely to use with video data. Instead, the present invention is well suited to use with audio-based data, image-based data, web page-based data, graphic data and the like (“media data”). Specifically, the present invention is directed towards any data in which scalable coding is combined with progressive encryption. In step 602 of FIG. 6, in one embodiment, the present invention recites receiving video data. In one embodiment, the video data is comprised of a stream of uncompressed video frames which are received by segmenter 702 of the encoder system 700 of FIG. 7.

In another embodiment of the present invention, the video data is comprised of prediction error video data generated by a video prediction unit (VPU). As shown FIG. 8, in one embodiment of the present invention encoder system 700 has a VPU 800 coupled thereto. VPU 800 generates and forwards prediction error video data to segmenter 702 of encoder system 700. Although VPU 800 of FIG. 8 is disposed outside of encoding system 700, the present invention is also well suited to having VPU 800 integral with encoding system 700. FIG. 9 illustrates one embodiment of the present invention in which VPU 800 is integral with encoding system 700.

With reference now to step 604 of FIG. 6, the present embodiment then segments the received video data into corresponding regions. FIG. 10A provides a schematic depiction of a video frame 1000. Video data corresponding to video frame 1000 is received by segmenter 702 of FIGS. 7, 8, and 9. FIG. 10B depicts the same video frame 1000 after segmenter 702 has segmented video frame 1000 into corresponding regions 1002, 1004, 1006, 1008, 1010, and 1012. Although such a quantity and configuration of regions is shown in FIG. 10B, such a tiling quantity and configuration is intended to be exemplary only. As one example, FIG. 10C illustrates another example of segmentation in which segmenter 702 has segmented video frame 100 into various non-rectangular regions 1014, 1016, 1018, 1020, and 1022. As another example, FIG. 10D illustrates another example of segmentation in which segmenter 702 has segmented video frame 100 into various non-rectangular and overlapping regions 1024, 1026, 1028, 1030, and 1032. The overlapping portions are denoted by dotted lines. The present invention is also well suited to an approach in which segmenter 702 has various rectangular regions configured in an overlapping arrangement. Furthermore, the present invention is also well suited to an embodiment in which the regions change from frame to frame. Such an embodiment is employed, for example, to track a foreground person as they move.

Referring now to step 606, encoder 704 of FIGS. 7, 8 and 9 then scalably encodes the regions into scalable video data. For purposes of the present Application, scalable coding is defined as a process which takes original data as input and creates scalably coded data as output, where the scalably coded data has the property that portions of it can be used to reconstruct the original data with various quality levels. Specifically, the scalably coded data is often thought of as an embedded bitstream. The first portion of the bitstream can be used to decode a baseline-quality reconstruction of the original data, without requiring any information from the remainder of the bitstream, and progressively larger portions of the bitstream can be used to decode improved reconstructions of the original data. That is, separate regions or regions of a video frame are encoded into one or more data packets. The scalable video data generated by the present embodiment has the property that a first small portion of the data can be decoded into baseline quality video, and larger portions can be decoded into improved quality video. It is this property that allows data packets to be transcoded to lower bitrates or spatial resolutions simply by truncating the data packet. This process of truncation will be discussed in further detail below.

With reference still to step 606, in one embodiment of the present invention each region is coded by encoder 704 into two portions: header data and scalable video data. Hence, in such an embodiment, each data packet contains header data and scalable video data. The header data describes, for example, the region (e.g. the location of the region within the video frame) that the data packet represents and other information used for subsequent transcoding and decoding operations in accordance with the present invention. Furthermore, in one embodiment, the header data contains information including a series of recommended truncation points for data packet transcoders. The scalable video data contains the actual coded video. In the case of intraframe coding, the video data may be the coded pixels; while in the case of interframe coding, it may be the motion vectors and coded residuals that result from motion-compensated prediction. In the present embodiments, scalable coding techniques are used in both cases to create an embedded or scalable data packet that can be truncated to lower the resolution or fidelity of the coded video data. In still another embodiment of the present invention, the scalably encoded video data is prepared by encoder 704 without corresponding header data.

As recited in step 608, the present embodiment then progressively encrypts the scalable video data to generate progressively encrypted scalable video data. That is, packetizer and encrypter 706 of FIGS. 7, 8, and 9 employs progressive encryption techniques to encrypt the scalable video data. For purposes of the present Application, progressive encryption is defined as a process which takes original data (plaintext) as input and creates progressively encrypted data (ciphertext) as output, where the progressively encrypted data has the property that the first portion can be decrypted alone, without requiring information from the remainder of the original data; and progressively larger portions can be decrypted with this same property, in which decryption can require data from earlier but not later portions of the bitstream. Progressive encryption techniques include, for example, cipher block chains or stream ciphers. These progressive encryption methods have the property that the first portion of the data is encrypted independently, then later portions are encrypted based on earlier portions. When properly matched with scalable coding and packetization, progressive encryption preserves the ability to transcode data packets with simple data packet truncation. More specifically, progressive encryption methods have the property that smaller blocks of data are encrypted progressively. While block code encryption with small block sizes is not very secure, progressive encryption methods add a degree of security by feeding encrypted data of earlier blocks into the encryption of a later block. Decryption can then be performed progressively as well. In one embodiment, the first small block of ciphertext is decrypted into plaintext by itself while later blocks of ciphertext depend on the decrypted plaintext from earlier blocks. Thus, earlier blocks of ciphertext can be decrypted without knowledge of the entire ciphertext segment. This progressive nature of cipher block chains and stream ciphers matches nicely with the progressive or embedded nature of scalable coding. Although encoding system 700 depicts a combined packetizer and encrypter module 706. Such a depiction is exemplary only, as encoding system 700 of the present invention is well suited to having separate and distinct packetizer and encrypter modules.

As was the case in prior art approaches, entire data packets were encrypted with one long block code. As a result, decryption was not possible unless it the data packet was received in its entirety. However, the present invention is using scalable data packets and it is desired to transcode the stream of scalable data packets by data packet truncation. Therefore, the present invention encrypts the data packets in a similarly progressive manner. Hence, unlike conventional approaches, the present invention is data packet loss resilient. That is, should a data packet be lost, decryption of the remaining data packets is not further complicated and is still readily achievable. This combination of scalable encoding and progressive encryption enables the advantageous transcoding operations described in detail below.

With reference still to step 608, in one embodiment of the present invention, while the payload data (i.e. the scalable video data) is encrypted progressively, the header data is left unencrypted so that transcoding nodes can use this information to make transcoding decisions. For example, in one embodiment, the unencrypted header contains information such as recommended truncation points within the encrypted payload data. In another embodiment, this header data is used to achieve near rate distortion (RD)-optimal bitrate reduction by intermediate transcoding nodes. Moreover, in the present embodiment, the transcoding nodes can use the header data to make transcoding decisions without requiring decryption of the progressively encrypted scalable video data or the header data. In yet another embodiment of the present invention the header data is encrypted to add additional security.

Referring now to step 610, the present invention then packetizes the progressively encrypted scalable video data. In one embodiment, a packetizer and encrypter 706 of FIGS. 7, 8, and 9 combine and packetize the unencrypted header data with the progressively encrypted scalable video data. The resulting secure scalable data packets are then available to be streamed to desired receivers. In another embodiment, packetizer and encrypter 706 packetizes the progressively encrypted scalable video data and the encrypted header data. Furthermore, in an embodiment which does not include header data, packetizer and encrypter 706 packetizes only the progressively encrypted scalable video data.

Encoding system 700 securely and scalably encodes video data. More specifically, encoding system 700 combines scalable coding with progressive encryption techniques. The resulting scalably encoded, progressively encrypted, and packetized video streams have the feature that subsequent transcoding operations such as bitrate reduction and spatial downsampling can be performed (via e.g. data packet truncation or data packet elimination) without decrypting the packetized data and thus while maintaining the security of the system. The present invention is also well suited to an embodiment in which only some, but not all, of the regions formed by segmenter 702 are ultimately forwarded from encoding system 700. As an example, in one embodiment of the foreground of a video data image is forwarded, as the background image may not have changed since a previous transmission, or perhaps the background image does not contain data of interest.

Decoding Method and System

Although specific steps are disclosed in flow chart 1100 of FIG. 11, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 11. In step 1102 of FIG. 11, the present invention receives a data packet containing progressively encrypted and scalably encoded video data. More specifically, decrypter 1202 of decoding system 1200, both of FIG. 12, receives the data packet containing progressively encrypted and scalably encoded video data. In one embodiment, the received data packet also includes header data wherein the header data provides information corresponding to the scalably encoded video data. In yet another embodiment, the received data packet also includes encrypted header data providing information corresponding to the scalably encoded video data.

As recited in step 1104, the present invention then decrypts the data packet containing the progressively encrypted and scalably encoded video data to generate scalably encoded regions. That is, decrypter 1202 of FIG. 12 decrypts the progressively encrypted and scalably encoded video data to generate scalably encoded regions. Furthermore, in an embodiment in which the received data packet includes encrypted header data, decrypter 1202 also decrypts the encrypted header data.

Referring now to step 1106, the present embodiment then decodes the scalably encoded regions to provide decoded regions. As described above in conjunction with the description of encoding system 700 of FIGS. 7, 8, and 9, a video frame 1000 as shown in FIG. 10A can be segmented in multiple corresponding regions 1002, 1004, 1006, 1008, 1010, and 1012 as shown in FIG. 10B.

At step 1108, the present invention then assembles the decoded regions to provide video data. Moreover, assembler 1206 of decoding system 1200 of FIG. 12 assembles the decoded regions to provide video data. In one embodiment of the present invention decoding system 1200 then provides as output, video data in the form of an uncompressed video stream. In another embodiment of the present invention, assembler 1206 outputs video data comprised of prediction error video data suitable for by a video prediction unit (VPU). As shown FIG. 13, in one embodiment of the present invention decoder system 1200 has a VPU 1300 coupled thereto. VPU 1300 uses the output of assembler 1206 to ultimately provide an uncompressed stream of video frame data. Although VPU 1300 of FIG. 13 is disposed outside of decoding system 1200, the present invention is also well suited to having VPU 1300 integral with decoding system 1200. FIG. 14 illustrates one embodiment of the present invention in which VPU 1300 is integral with decoding system 1200. Hence, the present invention provides a method and system for decoding video data which has been securely and scalably encoded.

Transcoding Method and System

FIG. 15A is a block diagram of an exemplary hybrid wired/wireless network 1500 upon which embodiments of the present invention may be practiced. In hybrid wired/wireless network 1500, media (e.g., video) data are streamed to fixed clients (stationary receiving nodes) via a wired link and to mobile clients (moving receiving nodes) via a wireless link.

In the present embodiment, hybrid wired/wireless network 1500 includes a wired sender (source 1510), a wired high-resolution receiver 1520, and a wireless medium-resolution receiver 1540. In this system, source 1510 generates a full-bandwidth, high-resolution video stream 1550 a that is sent to high-resolution receiver 1520. A transcoder 1530, placed at source 1510, at medium-resolution receiver 1540, or at an intermediate node such as a wired/wireless gateway, transcodes the stream 1550 a into a lower-bandwidth, medium-resolution video stream 1550 b which is then sent to medium-resolution receiver 1540.

FIG. 15B is a block diagram of an exemplary wireless network 1501 (e.g., a wireless appliance network) upon which embodiments of the present invention may be practiced. In wireless appliance networks, mobile senders and receivers communicate with one another over wireless links. A sender's coverage area is limited by the power of the transmitted signal. Relay devices can be used to extend the wireless coverage area when intended receivers are beyond the immediate coverage area of the sender. In the case of heterogeneous receivers (e.g., receiving nodes having different display, power, computational, and communication characteristics and capabilities), transcoders can be used to adapt a video stream for a particular receiver or communication link. Transcoding can be performed in a relay device or in a receiver which also acts as a relay. Transcoding can also be performed by the sender or by the receiving node.

In the present embodiment, wireless network 1501 includes a wireless sender (source 1510), a high-resolution receiver and transcoder 1560, and a medium-resolution (lower bandwidth) receiver 1540. In wireless network 1501, the high-resolution receiver 1560 receives and transcodes the high-resolution video stream 1550 a, and relays the resulting lower-bandwidth stream 1550 b to the medium-resolution receiver 1540.

Referring to FIGS. 15A and 15B, both hybrid wired/wireless network 1500 and wireless network 1501 use network transcoders to transcode video streams 1550 a into lower bandwidth streams 1550 b that match the display capabilities of the target wireless nodes (e.g., medium-resolution receiver 1540). Generally speaking, these networks illustrate how network transcoding can enable efficient use of wireless spectrum and receiver resources by transcoding media (e.g., video) streams into formats better suited for transmission over particular channels and for the capabilities of the receiving nodes.

FIG. 16 is a block diagram of a system 1600 including a source node 1610, an intermediate (transcoder) node 1620, and a receiving node 1630 in accordance with one embodiment of the present invention. In this embodiment, transcoder 1620 is a separate node transposed between source node 1610 and receiving node 1630. However, the functions performed by transcoder 1620 may instead be performed by source node 1610 or by receiving node 1630.

In the present embodiment, source node 1610 encodes and/or encrypts a stream of data packets and sends these data packets to transcoder 1620, as described above. In one embodiment, each of the data packets in the stream has a header portion and a payload portion (see FIG. 20, below); in another embodiment, the data packet has only a payload portion (see FIG. 21, below). The payload portion carries the data, while the header portion carries information that is used by transcoder 1620 to transcode the payload portion. A data packet, including the information carried by the header portion, and the transcoding method used by transcoder 1620 are further described below. In one embodiment, only the payload portion is encrypted and encoded. In another embodiment, the payload portion is encrypted and encoded, and the header portion is also encrypted.

In the present embodiment, transcoder 1620 performs a transcoding function on the data packets received from source node 1610. The transcoding function performed by transcoder 1620 is described in conjunction with FIG. 19, below. The purpose of the transcoding function is to configure the stream of data packets according to the attributes downstream of transcoder 1620, such as the attributes of the receiving node 1630 or the attributes of communication channel 1625 linking transcoder 1620 and receiving node 1630. The transcoding function can include, for example, truncation of the data packets or elimination of certain data packets from the stream. In the case in which the stream is already configured for the receiving node 1630 or for communication channel 1625, the transcoding function consists of a pass-through of the data packets in the stream without modification.

Of particular significance, in accordance with the present invention, transcoder 1620 performs a transcoding function without decrypting and/or decoding the data packets (specifically, the media data in the data packets). In the embodiment in which the data packets have a header portion and a payload portion, and where the header portion is encrypted, transcoder 1620 only decrypts the header portion. In either case, in comparison to a conventional transcoder, transcoder 1620 of the present invention requires less computational resources because there is no need to decrypt the media data. In addition, the present invention provides end-to-end security while enabling very low complexity transcoding to be performed at intermediate, possibly untrusted, nodes without compromising the security of the media data.

Continuing with reference to FIG. 16, transcoder 1620 has knowledge of the attributes of receiving node 1630 and/or communication channel 1625. These attributes include, but are not limited to, the display, power, communication and computational capabilities and characteristics of receiving node 1630, or the available bandwidth on communication channel 1625. For example, in one embodiment, transcoder 1620 receives the attribute information from receiving node 1630, or transcoder 1620 reads this information from receiving node 1630. In another embodiment, transcoder 1620 may be implemented as a router in a network; the router can determine if there is congestion on the next “hop” and transcode the stream of data packets accordingly.

In the present embodiment, after transcoding, transcoder 1620 sends the resultant stream of data packets, comprising the encoded and encrypted data packets, to receiving node 1630.

FIG. 17 is a block diagram of one embodiment of a transcoder device 1620 upon which embodiments of the present invention may be practiced. In this embodiment, transcoder 1620 includes a receiver 1710 and a transmitter 1720 for receiving a stream of data packets from source node 1610 (FIG. 16) and for sending a stream of data packets to receiving node 1630 (FIG. 16), respectively. Receiver 1710 and transmitter 1720 are capable of either wired or wireless communication. Separate receivers and transmitters, one for wired communication and one for wireless communication, may also be used. It is appreciated that receiver 1710 and transmitter 1720 may be integrated as a single device (e.g., a transceiver).

Continuing with reference to FIG. 17, transcoder device 1620 may include an optional controller 1730 (e.g., a processor or microprocessor), an optional decrypter 1740, and an optional memory 1750, or a combination thereof. In one embodiment, decrypter 1740 is used to decrypt header information. In another embodiment, memory 1750 is used to accumulate data packets received from source node 1610 before they are forwarded to receiving node 1630 (FIG. 16).

FIGS. 18A, 18B, 18C, 18D and 18E are data flow diagrams illustrating various embodiments of a method for transcoding data packets in accordance with the present invention. In the embodiments of FIGS. 18A-D, the data packets each have a header portion and a payload portion; in the embodiment of FIG. 18E, the data packets do not have a header portion. In each of the embodiments of FIGS. 18A-E, the data packets (specifically, the media data) are encrypted and may be encoded. The embodiments of FIGS. 18A-E are separately described in order to more clearly describe certain aspects of the present invention; however, it is appreciated that the present invention may be implemented by combining elements of these embodiments.

In accordance with the present invention, the method for transcoding data packets is performed on the encrypted data packets; that is, the media data are not decrypted. Transcoding functions can include truncation of the data packets (specifically, the payload portions of the data packets), eliminating certain data packets from the stream, or passing the data packets through without modification.

With reference first to FIG. 18A, incoming encrypted and/or encoded data packets are received by transcoder 1620. In this embodiment, the header portion of each data packet is not encrypted. Transcoder 1620 reads the header portion, which contains information that can be used to make transcoding decisions. In one embodiment, the information in the header portion includes specification of the truncation points. In another embodiment, the truncation points are derived from the information provided in the header.

For example, the header portion may contain information specifying recommended points (e.g., a number of a bit) for truncating the payload portion of the data packets. It is appreciated that each data packet may have a different truncation point. The recommended truncation point can be selected using a variety of techniques. In one embodiment, the truncation point for each data packet is specified according to an analysis such as a rate-distortion (RD) analysis, so that the stream of data packets can be compressed to a rate that is RD optimal or near-RD optimal. In another embodiment, the header portion contains information that describes the RD curves generated by the RD analysis, and the truncation points are derived from further analysis of the RD curves.

In the present embodiment, RD optimal coding is achieved by generating an RD plot for each region of a video image, and then operating on all regions at the same slope that generates the desired total bitrate. Near-optimal transcoding can be achieved at the data packet level by placing the optimal RD cutoff points for a number of quality levels in the header portions of the data packets. Then, transcoder 1620 (FIG. 16) can truncate each packet at the appropriate cutoff point; thus, the resulting packets will contain the appropriate number of bits for each region of the image for the desired quality level. Transcoder 1620 reads each packet header, then truncates the packet at the appropriate point. For example, if three regions in an image are coded into separate packets, for each region three RD optimal truncation points are identified and their locations placed in the respective packet header. Transcoder 1620 can choose to operate at any of the three RD points (or points in between), and then can truncate each packet at the appropriate cutoff point.

The header portion may also contain information identifying each data packet by number, for example. Accordingly, transcoder 1620 can eliminate certain data packets from the stream; for example, if every other packet is to be eliminated (e.g., the odd-numbered packets), transcoder 1620 can use the header information to identify the odd-numbered data packets and eliminate those from the stream of data packets.

The embodiment of FIG. 18B is similar to that of FIG. 18A, except that the header portion of each data packet is encrypted. In this case, transcoder 1620 first decrypts the header portion, before reading the header information and operating on the stream of data packets as described above.

In the embodiment of FIG. 18C, data packets are accumulated in memory. That is, instead of a first-in/first-out type of approach, a subset of the data packets in the stream is accumulated and stored in memory (e.g., memory 1750 of FIG. 17) before they are forwarded to the receiving node. In this embodiment, the header information for all of the accumulated data packets in the subset is used to make transcoding decisions. The transcoding decisions are made based on the attributes of the receiving node 1630 or the attributes of the communication channel 1625 (FIG. 16), as described previously herein. It may be possible, and perhaps desirable, to configure the stream of data packets according to the attributes of the receiving node or communication channel without operating on every data packet in the stream. For example, instead of truncating all of the data packets in the subset, a decision may be made to truncate only a portion of the packets in the subset, or to truncate the packets at a point other than the recommended truncation point.

In the embodiment of FIG. 18D, transcoder 1620 receives information from the downstream receiving node (e.g., receiving node 1630 of FIG. 16). In one embodiment, the information describes attributes of receiving node 1630, such as its display, power, computational and communication capabilities and characteristics. Based on the information received from receiving node 1630, transcoder 1620 can make transcoding decisions based on the information in the header portions of the data packets. For example, transcoder 1620 can pick a truncation point depending on whether receiving node 1630 is a medium- or low-resolution device, and transcoder 1620 can choose not to modify the stream of data packets if receiving node 1630 is a high-resolution device. Similarly, transcoder 1620 can receive information describing the attributes of communication channel 1625 (FIG. 16)

In the embodiment of FIG. 18E, the incoming data packets do not have a header portion. Accordingly, transcoder 1620 makes transcoding decisions based on a predefined set of rules. That is, instead of truncating each data packet at a different point specified by the information in the header portion, transcoder 1620 may truncate all data packets in the stream at the same point, depending on the attributes of the receiving node or communication channel.

FIG. 19 is a flowchart of the steps in a process 1900 for transcoding data packets in accordance with one embodiment of the present invention. In one embodiment, process 1900 is implemented by transcoder device 1620 (FIG. 17) as computer-readable program instructions stored in memory 1750 and executed by controller 1730. Although specific steps are disclosed in of FIG. 19, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 19.

In step 1910 of FIG. 19, a stream of data packets is received from a source node (e.g., source 1610 of FIG. 16). In the present embodiment, the data packets include encrypted data. In one embodiment, the data are also encoded. In another embodiment, the data packets include a header portion and a payload portion. In one embodiment, the header portion is also encrypted.

In step 1915 of FIG. 19, in one embodiment, information describing the attributes of a downstream receiving node (e.g., receiving node 1630 of FIG. 16) or communication channel (e.g., communication channel 1625 of FIG. 16) is received. In another embodiment, the attributes of receiving node 1630 or communication channel 1625 are already known.

In step 1920 of FIG. 19, a transcoding function is performed on the stream of data packets to configure the stream according to the attributes of receiving node 1630. Significantly, the transcoding function is performed without decrypting the data in the data packets. In one embodiment, the transcoding function is performed on information provided by the header portion of each data packet. In one such embodiment, the header information provides recommended truncation points for the payload portion of the respective data packet. In another embodiment, the truncation points are derived from the information provided in the header portion.

In step 1922, in one embodiment, the transcoding function eliminates certain data packets from the stream. In step 1924, in one embodiment, the transcoding function truncates the data in the data packets. It is appreciated that each data packet may have a different truncation point. In step 1926, in one embodiment, the transcoding function passes the data packets through without modification.

In step 1930, the transcoded data packets (still encrypted and/or encoded) are sent to receiving node 1630.

In summary, the above-listed embodiment of the present invention provides a secure method and system for transcoding data for a variety of downstream attributes, such as the attributes of receiving nodes having different capabilities and characteristics or the attributes of the communication between the transcoder and a receiving node. Because the encrypted data do not need to be decrypted and then encrypted again, the computational resources needed for transcoding the stream of data packets is significantly reduced, and the security of the data is not compromised.

Secure Scalable Data Packet

With reference now to FIG. 20, a schematic representation of a data packet 2000 formed in accordance with one embodiment of the present invention is shown. Furthermore, as mentioned above, for purposes of clarity and brevity, the following discussion and examples will specifically deal with video data. The present invention, however, is not limited solely to use with video data. Instead, the present invention is well suited to use with audio-based data, image-based data, web page-based data, and the like. It will be understood that in the present embodiments, data packet 2000 is generated by encoding system 700 of FIGS. 7, 8, and 9, operated on by transcoder 1620 of FIGS. 16, 18A, 18B, 18C, 18D, and 18E, and then ultimately forwarded to decoding system 1200 of FIGS. 12, 13, and 14. During the aforementioned process, data packet 2000 is stored on computer readable media residing in, and causes a functional change or directs the operation of, the devices (e.g. general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, stand alone computer systems, and the like) in which, for example, transcoder 1620 and/or decoder 1200 are implemented.

In the embodiment of FIG. 20, data packet 2000 includes header data portion 2002 and scalably encoded, progressively encrypted video data portion 2004. As mentioned above, header data portion 2002 includes information that is used by transcoder 1620 to transcode the scalably encoded, progressively encrypted video data portion 2004. For example, header data portion 2002 may contain information specifying recommended points (e.g., a number of a bit) for truncating the payload portion (i.e. the scalably encoded, progressively encrypted video data portion 2004) of data packet 2000. Header data portion 2002 may also contain information identifying each data packet by number, for example. Accordingly, transcoder 1620 can eliminate certain data packets from the stream; for example, if every other packet is to be eliminated (e.g., the odd-numbered packets), transcoder 1620 can use the information in header data portion 2002 to identify the odd-numbered data packets and eliminate those from the stream of data packets.

With reference still to FIG. 20, data packet 2000 also includes potential truncation points 2006, 2008, and 2010 within scalably encoded, progressively encrypted video data portion 2004. Although such truncation points are shown in FIG. 20, the configuration of truncation points 2006, 2008, and 2010, is exemplary only. That is, the present invention is well suited to having a lesser of greater number of truncation points, and to having the truncation points located other than where shown in FIG. 20. Again, as mentioned above, truncation points 2006, 2008, and 2010 are used by transcoder 1620 during its operation on packet 2000. Additionally, in one embodiment of the present invention, header data portion 2002 is encrypted.

In the embodiment of FIG. 21, data packet 2100 does not include a header data portion, and instead includes only scalably encoded, progressively encrypted video data portion 2104. With reference still to FIG. 21, data packet 2100 also includes potential truncation points 2104, 2106, and 2108 within scalably encoded, progressively encrypted video data portion 2104. Although such truncation points are shown in FIG. 21, the configuration of truncation points 2104, 2106, and 2108, is exemplary only. That is, the present invention is well suited to having a lesser of greater number of truncation points, and to having the truncation points located other than where shown in FIG. 21. Again, as mentioned above, truncation points 2104, 2106, and 2108 are used by transcoder 1620 during its operation on packet 2100.

Thus, the present invention provides, in one embodiment, a data packet format which enables secure and scalable encoding, transcoding, and decoding of data.

General Description of the Present Scalable Streaming Invention

With reference next to FIG. 22, FIG. 27, and FIG. 35, flow charts 2200, 2700, and 3500, respectively, illustrate exemplary steps used by the various embodiments of present invention. Flow charts 2200, 2700, and 3500 include processes of the present invention which, in one embodiment, are carried out by a processor under the control of computer-readable and computer-executable instructions. The computer-readable and computer-executable instructions reside, for example, in data storage features such as computer usable volatile memory 506, computer usable non-volatile memory 508, and/or data storage device 510 of FIG. 5. The computer-readable and computer-executable instructions are used to control or operate in conjunction with, for example, central processing unit 504 of FIG. 5.

As an overview, the present invention is directed towards any data which can be scalably encoded. For purposes of the present Application, scalable coding is defined as a process which takes original data as input and creates scalably coded data as output, where the scalably coded data has the property that portions of it can be used to reconstruct the original data with various quality levels. Specifically, the scalably coded data is often thought of as an embedded bitstream. The first portion of the bitstream can be used to decode a baseline-quality reconstruction of the original data, without requiring any information from the remainder of the bitstream, and progressively larger portions of the bitstream can be used to decode improved reconstructions of the original data.

Encoding Method and System

Although specific steps are disclosed in flow chart 2200 of FIG. 22, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 22. Additionally, for purposes of clarity and brevity, the following discussion and examples will specifically deal with video data. The present invention, however, is not limited solely to use with video data. Instead, the present invention is well suited to use with audio-based data, image-based data, web page-based data, graphic data and the like (“media data”). Specifically, the present invention is directed towards any data upon which scalable coding is performed. In step 2202 of FIG. 6, in one embodiment, the present invention recites receiving video data. In one embodiment, the video data is comprised of a stream of uncompressed video frames which are received by segmenter 2302 of the encoder system 2300 of FIG. 23.

In another embodiment of the present invention, the video data is comprised of prediction error video data generated by a video prediction unit (VPU). As shown FIG. 24, in one embodiment of the present invention encoder system 2300 has a VPU 2400 coupled thereto. VPU 2400 generates and forwards prediction error video data to segmenter 2302 of encoder system 2300. Although VPU 2400 of FIG. 24 is disposed outside of encoding system 2300, the present invention is also well suited to having VPU 2400 integral with encoding system 2300. FIG. 25 illustrates one embodiment of the present invention in which VPU 2400 is integral with encoding system 2300.

With reference now to step 2204 of FIG. 22, the present embodiment then segments the received video data into corresponding regions. FIG. 26A provides a schematic depiction of a video frame 2600. Video data corresponding to video frame 2600 is received by segmenter 2302 of FIGS. 23, 24, and 25. FIG. 26B depicts the same video frame 2600 after segmenter 2302 has segmented video frame 2600 into corresponding regions 2602, 2604, 2606, 2608, 2610, and 2612. Although such a quantity and configuration of regions is shown in FIG. 26B, such a tiling quantity and configuration is intended to be exemplary only. As one example, FIG. 26C illustrates another example of segmentation in which segmenter 2302 has segmented video frame 2600 into various non-rectangular regions 2614, 2616, 2618, 2620, and 2622. As another example, FIG. 26D illustrates another example of segmentation in which segmenter 2302 has segmented video frame 2600 into various non-rectangular and overlapping regions 2624, 2626, 2628, 2630, and 2632. The overlapping portions are denoted by dotted lines. The present invention is also well suited to an approach in which segmenter 2302 has various rectangular regions configured in an overlapping arrangement. Furthermore, the present invention is also well suited to an embodiment in which the regions change from frame to frame. Such an embodiment is employed, for example, to track a foreground person as they move.

Referring now to step 2206, encoder 2304 of FIGS. 23, 24 and 25 then scalably encodes the regions into scalable video data. For purposes of the present Application, scalable coding is defined as a process which takes original data as input and creates scalably coded data as output, where the scalably coded data has the property that portions of it can be used to reconstruct the original data with various quality levels. Specifically, the scalably coded data is often thought of as an embedded bitstream. The first portion of the bitstream can be used to decode a baseline-quality reconstruction of the original data, without requiring any information from the remainder of the bitstream, and progressively larger portions of the bitstream can be used to decode improved reconstructions of the original data. That is, separate regions or regions of a video frame are encoded into one or more data packets. The scalable video data generated by the present embodiment has the property that a first small portion of the data can be decoded into baseline quality video, and larger portions can be decoded into improved quality video. It is this property that allows data packets to be transcoded to lower bitrates or spatial resolutions simply by truncating the data packet. This process of truncation will be discussed in further detail below.

With reference still to step 2206, in one embodiment of the present invention each region is coded by encoder 2304 into two portions: header data and scalable video data. Hence, in such an embodiment, each data packet contains header data and scalable video data. The header data describes, for example, the region (e.g. the location of the region within the video frame) that the data packet represents and other information used for subsequent transcoding and decoding operations in accordance with the present invention. Furthermore, in one embodiment, the header data contains information including a series of recommended truncation points for data packet transcoders. The scalable video data contains the actual coded video. In the case of intraframe coding, the video data may be the coded pixels; while in the case of interframe coding, it may be the motion vectors and coded residuals that result from motion-compensated prediction. In the present embodiments, scalable coding techniques are used in both cases to create an embedded or scalable data packet that can be truncated to lower the resolution or fidelity of the coded video data. In still another embodiment of the present invention, the scalably encoded video data is prepared by encoder 2304 without corresponding header data.

Referring now to step 2208, the present invention then packetizes the scalable video data. In one embodiment, a packetizer 2306 of FIGS. 23, 24, and 25 combine and packetize the header data with the scalable video data. The resulting scalable data packets are then available to be streamed to desired receivers. In another embodiment, packetizer 2306 separately packetizes the scalable video data and the header data. Furthermore, in an embodiment which does not include header data, packetizer 2306 packetizes only the scalable video data.

Encoding system 2300 scalably encodes video data. The resulting scalably encoded and packetized video streams have the feature that subsequent transcoding operations such as bitrate reduction and spatial downsampling can be performed (via e.g. data packet truncation or data packet elimination) without requiring encrypting and/or decrypting of the packetized data as is required in some prior art schemes. The present invention is also well suited to an embodiment in which only some, but not all, of the regions formed by segmenter 2302 are ultimately forwarded from encoding system 2300. As an example, in one embodiment of the foreground of a video data image is forwarded, as the background image may not have changed since a previous transmission, or perhaps the background image does not contain data of interest.

Decoding Method and System

Although specific steps are disclosed in flow chart 2700 of FIG. 27, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 27. In step 2702 of FIG. 27, the present invention receives a data packet containing scalably encoded video data. More specifically, decoder 2804 of decoding system 2800, both of FIG. 28, receives the data packet containing scalably encoded video data. In one embodiment, the received data packet also includes header data wherein the header data provides information corresponding to the scalably encoded video data.

Referring now to step 2704, the present embodiment then decodes the scalably encoded regions to provide decoded regions. As described above in conjunction with the description of encoding system 2300 of FIGS. 23, 24, and 25, a video frame 2600 as shown in FIG. 26A can be segmented in multiple corresponding regions 2602, 2604, 2606, 2608, 2610, and 2612 as shown in FIG. 26B.

At step 2706, the present invention then assembles the decoded regions to provide video data. Moreover, assembler 2806 of decoding system 2800 of FIG. 28 assembles the decoded regions to provide video data. In one embodiment of the present invention decoding system 2800 then provides as output, video data in the form of an uncompressed video stream. In another embodiment of the present invention, assembler 2806 outputs video data comprised of prediction error video data suitable for by a video prediction unit (VPU). As shown FIG. 29, in one embodiment of the present invention decoder system 2800 has a VPU 2900 coupled thereto. VPU 2900 uses the output of assembler 2806 to ultimately provide an uncompressed stream of video frame data. Although VPU 2900 of FIG. 29 is disposed outside of decoding system 2800, the present invention is also well suited to having VPU 2900 integral with decoding system 2800. FIG. 30 illustrates one embodiment of the present invention in which VPU 2900 is integral with decoding system 2800. Hence, the present invention provides a method and system for decoding video data which has been scalably encoded.

Transcoding Method and System

FIG. 31A is a block diagram of an exemplary hybrid wired/wireless network 3100 upon which embodiments of the present invention may be practiced. In hybrid wired/wireless network 3100, media (e.g., video) data are streamed to fixed clients (stationary receiving nodes) via a wired link and to mobile clients (moving receiving nodes) via a wireless link.

In the present embodiment, hybrid wired/wireless network 3100 includes a wired sender (source 3110), a wired high-resolution receiver 3120, and a wireless medium-resolution receiver 3140. In this system, source 3110 generates a full-bandwidth, high-resolution video stream 3150 a that is sent to high-resolution receiver 3120. A transcoder 3130, placed at source 3110, at medium-resolution receiver 3140, or at an intermediate node such as a wired/wireless gateway, transcodes the stream 3150 a into a lower-bandwidth, medium-resolution video stream 3150 b which is then sent to medium-resolution receiver 3140.

FIG. 31B is a block diagram of an exemplary wireless network 1501 (e.g., a wireless appliance network) upon which embodiments of the present invention may be practiced. In wireless appliance networks, mobile senders and receivers communicate with one another over wireless links. A sender's coverage area is limited by the power of the transmitted signal. Relay devices can be used to extend the wireless coverage area when intended receivers are beyond the immediate coverage area of the sender. In the case of heterogeneous receivers (e.g., receiving nodes having different display, power, computational, and communication characteristics and capabilities), transcoders can be used to adapt a video stream for a particular receiver or communication link. Transcoding can be performed in a relay device or in a receiver which also acts as a relay. Transcoding can also be performed by the sender or by the receiving node.

In the present embodiment, wireless network 3101 includes a wireless sender (source 3110), a high-resolution receiver and transcoder 3160, and a medium-resolution (lower bandwidth) receiver 3140. In wireless network 3101, the high-resolution receiver 3160 receives and transcodes the high-resolution video stream 3150 a, and relays the resulting lower-bandwidth stream 3150 b to the medium-resolution receiver 3140.

Referring to FIGS. 31A and 31B, both hybrid wired/wireless network 3100 and wireless network 3101 use network transcoders to transcode video streams 3150 a into lower bandwidth streams 3150 b that match the display capabilities of the target wireless nodes (e.g., medium-resolution receiver 3140). Generally speaking, these networks illustrate how network transcoding can enable efficient use of wireless spectrum and receiver resources by transcoding media (e.g., video) streams into formats better suited for transmission over particular channels and for the capabilities of the receiving nodes.

FIG. 32 is a block diagram of a system 3200 including a source node 3210, an intermediate (transcoder) node 3220, and a receiving node 3230 in accordance with one embodiment of the present invention. In this embodiment, transcoder 3220 is a separate node transposed between source node 3210 and receiving node 3230. However, the functions performed by transcoder 3220 may instead be performed by source node 3210 or by receiving node 3230.

In the present embodiment, source node 3210 encodes a stream of data packets and sends these data packets to transcoder 3220, as described above. In one embodiment, each of the data packets in the stream has a header portion and a payload portion (see FIG. 36, below); in another embodiment, the data packet has only a payload portion (see FIG. 37, below). The payload portion carries the data, while the header portion carries information that is used by transcoder 3220 to transcode the payload portion. A data packet, including the information carried by the header portion, and the transcoding method used by transcoder 3220 are further described below. In one embodiment, only the payload portion is encoded. In another embodiment, the payload portion is encoded, and the header portion is also encoded.

In the present embodiment, transcoder 3220 performs a transcoding function on the data packets received from source node 3210. The transcoding function performed by transcoder 3220 is described in conjunction with FIG. 35, below. The purpose of the transcoding function is to configure the stream of data packets according to the attributes downstream of transcoder 3220, such as the attributes of the receiving node 3230 or the attributes of communication channel 3225 linking transcoder 3220 and receiving node 3230. The transcoding function can include, for example, truncation of the data packets or elimination of certain data packets from the stream. In the case in which the stream is already configured for the receiving node 3230 or for communication channel 3225, the transcoding function consists of a pass-through of the data packets in the stream without modification.

Continuing with reference to FIG. 32, transcoder 3220 has knowledge of the attributes of receiving node 3230 and/or communication channel 3225. These attributes include, but are not limited to, the display, power, communication and computational capabilities and characteristics of receiving node 3230, or the available bandwidth on communication channel 3225. For example, in one embodiment, transcoder 3220 receives the attribute information from receiving node 3230, or transcoder 3220 reads this information from receiving node 3230. In another embodiment, transcoder 3220 may be implemented as a router in a network; the router can determine if there is congestion on the next “hop” and transcode the stream of data packets accordingly.

In the present embodiment, after transcoding, transcoder 3220 sends the resultant stream of data packets, comprising the encoded data packets, to receiving node 3230.

FIG. 33 is a block diagram of one embodiment of a transcoder device 3220 upon which embodiments of the present invention may be practiced. In this embodiment, transcoder 3220 includes a receiver 3310 and a transmitter 3320 for receiving a stream of data packets from source node 3210 (FIG. 32) and for sending a stream of data packets to receiving node 3230 (FIG. 32), respectively. Receiver 3310 and transmitter 3320 are capable of either wired or wireless communication. Separate receivers and transmitters, one for wired communication and one for wireless communication, may also be used. It is appreciated that receiver 3310 and transmitter 3320 may be integrated as a single device (e.g., a transceiver).

Continuing with reference to FIG. 33, transcoder device 3220 may include an optional controller 3330 (e.g., a processor or microprocessor), and an optional memory 3350, or a combination thereof. In another embodiment, memory 3350 is used to accumulate data packets received from source node 3210 before they are forwarded to receiving node 3230 (FIG. 32).

FIGS. 34A, 34B, 34C and 34D are data flow diagrams illustrating various embodiments of a method for transcoding data packets in accordance with the present invention. In the embodiments of FIGS. 34A-D, the data packets each have a header portion and a payload portion; in the embodiment of FIG. 34D, the data packets do not have a header portion. In each of the embodiments of FIGS. 34A-D, the data packets (specifically, the media data) may be encoded. The embodiments of FIGS. 34A-D are separately described in order to more clearly describe certain aspects of the present invention; however, it is appreciated that the present invention may be implemented by combining elements of these embodiments.

In accordance with the present invention, the method for transcoding data packets is performed on the data packets. Transcoding functions can include truncation of the data packets (specifically, the payload portions of the data packets), eliminating certain data packets from the stream, or passing the data packets through without modification.

With reference first to FIG. 34A, incoming encoded data packets are received by transcoder 3220. Transcoder 3220 reads the header portion, which contains information that can be used to make transcoding decisions. In one embodiment, the information in the header portion includes specification of the truncation points. In another embodiment, the truncation points are derived from the information provided in the header.

For example, the header portion may contain information specifying recommended points (e.g., a number of a bit) for truncating the payload portion of the data packets. It is appreciated that each data packet may have a different truncation point. The recommended truncation point can be selected using a variety of techniques. In one embodiment, the truncation point for each data packet is specified according to an analysis such as a rate-distortion (RD) analysis, so that the stream of data packets can be compressed to a rate that is RD optimal or near-RD optimal. In another embodiment, the header portion contains information that describes the RD curves generated by the RD analysis, and the truncation points are derived from further analysis of the RD curves.

In the present embodiment, RD optimal coding is achieved by generating an RD plot for each region of a video image, and then operating on all regions at the same slope that generates the desired total bitrate. Near-optimal transcoding can be achieved at the data packet level by placing the optimal RD cutoff points for a number of quality levels in the header portions of the data packets. Then, transcoder 3220 (FIG. 32) can truncate each packet at the appropriate cutoff point; thus, the resulting packets will contain the appropriate number of bits for each region of the image for the desired quality level. Transcoder 3220 reads each packet header, then truncates the packet at the appropriate point. For example, if three regions in an image are coded into separate packets, for each region three RD optimal truncation points are identified and their locations placed in the respective packet header. Transcoder 3220 can choose to operate at any of the three RD points (or points in between), and then can truncate each packet at the appropriate cutoff point.

The header portion may also contain information identifying each data packet by number, for example. Accordingly, transcoder 3220 can eliminate certain data packets from the stream; for example, if every other packet is to be eliminated (e.g., the odd-numbered packets), transcoder 3220 can use the header information to identify the odd-numbered data packets and eliminate those from the stream of data packets.

In the embodiment of FIG. 34B, data packets are accumulated in memory. That is, instead of a first-in/first-out type of approach, a subset of the data packets in the stream is accumulated and stored in memory (e.g., memory 3350 of FIG. 33) before they are forwarded to the receiving node. In this embodiment, the header information for all of the accumulated data packets in the subset is used to make transcoding decisions. The transcoding decisions are made based on the attributes of the receiving node 3230 or the attributes of the communication channel 3225 (FIG. 32), as described previously herein. It may be possible, and perhaps desirable, to configure the stream of data packets according to the attributes of the receiving node or communication channel without operating on every data packet in the stream. For example, instead of truncating all of the data packets in the subset, a decision may be made to truncate only a portion of the packets in the subset, or to truncate the packets at a point other than the recommended truncation point.

In the embodiment of FIG. 34C, transcoder 3220 receives information from the downstream receiving node (e.g., receiving node 3230 of FIG. 32). In one embodiment, the information describes attributes of receiving node 3230, such as its display, power, computational and communication capabilities and characteristics. Based on the information received from receiving node 3230, transcoder 3220 can make transcoding decisions based on the information in the header portions of the data packets. For example, transcoder 3220 can pick a truncation point depending on whether receiving node 3230 is a medium- or low-resolution device, and transcoder 3220 can choose not to modify the stream of data packets if receiving node 3230 is a high-resolution device. Similarly, transcoder 3220 can receive information describing the attributes of communication channel 3225 (FIG. 32)

In the embodiment of FIG. 34D, the incoming data packets do not have a header portion. Accordingly, transcoder 3220 makes transcoding decisions based on a predefined set of rules. That is, instead of truncating each data packet at a different point specified by the information in the header portion, transcoder 3220 may truncate all data packets in the stream at the same point, depending on the attributes of the receiving node or communication channel.

FIG. 35 is a flowchart of the steps in a process 3500 for transcoding data packets in accordance with one embodiment of the present invention. In one embodiment, process 3500 is implemented by transcoder device 3220 (FIG. 33) as computer-readable program instructions stored in memory 3350 and executed by controller 3330. Although specific steps are disclosed in of FIG. 35, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 35.

In step 3510 of FIG. 35, a stream of data packets is received from a source node (e.g., source 3210 of FIG. 32). In one embodiment, the data are encoded. In another embodiment, the data packets include a header portion and a payload portion.

In step 3515 of FIG. 35, in one embodiment, information describing the attributes of a downstream receiving node (e.g., receiving node 3230 of FIG. 32) or communication channel (e.g., communication channel 3225 of FIG. 32) is received. In another embodiment, the attributes of receiving node 3230 or communication channel 3225 are already known.

In step 3520 of FIG. 35, a transcoding function is performed on the stream of data packets to configure the stream according to the attributes of receiving node 3230. In one embodiment, the transcoding function is performed on information provided by the header portion of each data packet. In one such embodiment, the header information provides recommended truncation points for the payload portion of the respective data packet. In another embodiment, the truncation points are derived from the information provided in the header portion.

In step 3522, in one embodiment, the transcoding function eliminates certain data packets from the stream. In step 3524, in one embodiment, the transcoding function truncates the data in the data packets. It is appreciated that each data packet may have a different truncation point. In step 3526, in one embodiment, the transcoding function passes the data packets through without modification.

In step 3530, the transcoded data packets (still encoded) are sent to receiving node 3230.

In summary, the above-listed embodiment of the present invention provides a method and system for transcoding data for a variety of downstream attributes, such as the attributes of receiving nodes having different capabilities and characteristics or the attributes of the communication between the transcoder and a receiving node.

Scalable Data Packet

With reference now to FIG. 36, a schematic representation of a data packet 3600 formed in accordance with one embodiment of the present invention is shown. Furthermore, as mentioned above, for purposes of clarity and brevity, the following discussion and examples will specifically deal with video data. The present invention, however, is not limited solely to use with video data. Instead, the present invention is well suited to use with audio-based data, image-based data, web page-based data, and the like. It will be understood that in the present embodiments, data packet 3600 is generated by encoding system 2300 of FIGS. 23, 24, and 25, operated on by transcoder 3220 of FIGS. 32, 34A, 34B, 34C, and 34D, and then ultimately forwarded to decoding system 2800 of FIGS. 28, 29, and 30. During the aforementioned process, data packet 2600 is stored on computer readable media residing in, and causes a functional change or directs the operation of, the devices (e.g. general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, stand alone computer systems, and the like) in which, for example, transcoder 3220 and/or decoder 2800 are implemented.

In the embodiment of FIG. 36, data packet 3600 includes header data portion 3602 and scalably encoded video data portion 3604. As mentioned above, header data portion 3602 includes information that is used by transcoder 3220 to transcode the scalably encoded video data portion 3604. For example, header data portion 3602 may contain information specifying recommended points (e.g., a number of a bit) for truncating the payload portion (i.e. the scalably encoded video data portion 3604) of data packet 3600. Header data portion 3602 may also contain information identifying each data packet by number, for example. Accordingly, transcoder 3220 can eliminate certain data packets from the stream; for example, if every other packet is to be eliminated (e.g., the odd-numbered packets), transcoder 3220 can use the information in header data portion 3602 to identify the odd-numbered data packets and eliminate those from the stream of data packets.

With reference still to FIG. 36, data packet 3600 also includes potential truncation points 3606, 3608, and 3610 within scalably encoded video data portion 3604. Although such truncation points are shown in FIG. 36, the configuration of truncation points 3606, 3608, and 3610, is exemplary only. That is, the present invention is well suited to having a lesser of greater number of truncation points, and to having the truncation points located other than where shown in FIG. 36. Again, as mentioned above, truncation points 3606, 3608, and 3610 are used by transcoder 3220 during its operation on packet 3600.

In the embodiment of FIG. 37, data packet 3700 does not include a header data portion, and instead includes only scalably encoded video data portion 3702. With reference still to FIG. 37, data packet 3700 also includes potential truncation points 3704, 3706, and 3708 within scalably encoded video data portion 3704. Although such truncation points are shown in FIG. 37, the configuration of truncation points 3704, 3706, and 3708, is exemplary only. That is, the present invention is well suited to having a lesser of greater number of truncation points, and to having the truncation points located other than where shown in FIG. 37. Again, as mentioned above, truncation points 3704, 3706, and 3708 are used by transcoder 3220 during its operation on packet 3700.

Many types of scalable encoders can be used in conjunction with the various embodiments of the present invention. These scalable encoders can use intra-frame or inter-frame encoding. They can also use various types of scalability with different levels of granularity. As one example, JPEG-2000 can be employed in conjunction with the present embodiments because it was originally designed with the concepts of tiling (to enable random access) and scalability in mind. JPEG-2000 segments each image into tiles, then codes each tile using SNR (signal-to-noise ratio) or spatially scalable techniques. The coded data are placed in a file format, but without consideration of network packetization. When using such a scalable encoder, one embodiment of the present invention performs encoding in such a way as to produce independent scalable packets from scalable data; furthermore, in another embodiment appropriate header information can be added to the independent scalable packets to provide hints to downstream transcoders.

The JPEG-2000 standard evolved from EBCOT which uses a concept of Post-Compression Rate Distortion (PCRD) optimization to optimally code an image into a bitstream with a desired target bitrate. This is done by gathering rate distortion (RD) curve characteristics for different codeblocks, and coding each codeblock into an embedded bitstream. Specific target bitrates are achieved by extracting the appropriate RD-optimal portions of data from each codeblock and reorganizing these into the final embedded bitstream.

In JPEG-2000 and EBCOT, the codeblock RD information is used to optimally encode an image into a desired target bitrate. In accordance with various embodiments of the present invention, this information is used to calculate truncation points that can be included in packet headers to provide hints to downstream transcoders for bitrate reduction. By using this header information, transcoders can perform RD-optimal transcoding across packets.

As another example, 3D sub-band encoding can also be easily employed in conjunction with various embodiments of the present invention. For example, one approach uses a 3D sub-band encoder to encode video into packets such that each packet is decodable, of approximately equal importance, and embedded- or bitstream-scalable. In various embodiments, the present invention enables an intermediate node to perform transcoding by either truncating or discarding packets. Furthermore, recommended trunction points may be placed in the header of each packet to enable RD-optimal transcoding across packets.

MPEG-4 FGS (Fine-Grain Scalability) is a scalable video coder that encodes video into scalably encoded video data. The coded data are placed in a file format, but without consideration of network packetization. When using such a scalable encoder, one embodiment of the present invention performs encoding in such a way as to produce independent scalable packets from scalable data; furthermore, in another embodiment appropriate header information can be added to the independent scalable packets to provide hints to downstream transcoders.

Thus, the present invention provides, in one embodiment, a data packet format which enables scalable encoding, transcoding, and decoding of data.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. 

1. A non-transitory computer readable medium having computer readable instructions stored therein for causing a computer system to make a functional change in the operation of a transcoder, said instructions comprising: an encoder for encoding a data packet, said data packet comprising: a) a scalably encoded progressively encrypted data portion comprising at least one truncation point; and b) a header data portion corresponding to said scalably encoded progressively encrypted data portion, said header data portion including information that causes said transcoder to be able to efficiently transcode said scalably encoded progressively encrypted data portion, said information identifying said at least one truncation point within said scalably encoded data portion, said at least one truncation point enabling said transcoder to perform efficient transcoding of said data packet without decoding or decrypting said scalably encoded progressively encrypted data portion.
 2. The non-transitory computer readable medium of claim 1 wherein said information included in said header data portion of said data packet stored therein enables said transcoder to transcode said scalably encoded data portion without re-encoding said scalably encoded data portion.
 3. The non-transitory computer readable medium of claim 1 wherein said transcoder is selected from the group consisting of; general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, and stand alone computer systems.
 4. The non-transitory computer readable medium of claim 1 wherein said scalably encoded progressively encrypted data portion is selected from the group consisting of scalably encoded: video data, audio data, image data, graphic data, and web page data.
 5. A non-transitory computer readable medium having computer readable instructions stored therein for causing a computer system to make a functional change in the operation of a transcoder, said instructions comprising: an encoder for encoding a data packet, said data packet comprising: a) a scalably encoded progressively encrypted data portion, said scalably encoded progressively encrypted data portion comprising a truncation point identified therein, said truncation point enabling said transcoder to perform transcoding of said data packet; and b) a header data portion corresponding to said scalably encoded progressively encrypted data portion, said header data portion including information that causes said transcoder to be able to transcode said scalably encoded progressively encrypted data portion, said information identifying said truncation point within said scalably encoded data portion, said information included in said header data portion of said data packet stored therein enabling said transcoder to transcode said scalably encoded progressively encrypted data portion without decoding, decrypting, re-encrypting and re-encoding said scalably encoded progressively encrypted data portion.
 6. The non-transitory computer readable medium of claim 5 wherein said transcoder is selected from the group consisting of: general purpose networked computer systems, embedded computer systems, routers, switches; server devices, client devices, various intermediate devices/nodes, and stand alone computer systems.
 7. The non-transitory computer readable medium of claim 5 wherein said scalably encoded progressively encrypted data portion is selected from the group consisting of scalably encoded: video data, audio data, image data, graphic data, and web page data. 